I. Field of the Invention
The present invention relates to a high temperature electronic furnace suitable for converting fly ash into mineral wool.
Mineral wool is a fine fibrous "wool-like" material, typically made by blowing a small stream of molten rock or similar material, such as coal ash, with a jet or stream of fluid. The action of the jet of fluid blows the mineral stream into fine fibrous material which hardens before the fibers reach the floor.
The manufacturing process requires that the fly ash be melted and poured within critical temperature and pour rate tolerances. For example, fly ash typically melts and pours at around 2765 degrees Fahrenheit. However, at this temperature, the fly ash is a gummy mass, whereas at 2875 degrees Fahrenheit the fly ash flows like water. Moreover, the diameter of the resultant fibrous strains is highly dependent upon the temperature of the molten fly ash. Accordingly, it is essential that any furnace used to melt fly ash for the production of mineral wool have the capacity to control the temperature of the fly ash to precise tolerances, on the order of 5 to 10 degrees centigrade while processing large continuous volumes of fly ash--on the order of 40,000 lbs/hr for weeks at a time. However, no known prior art furnace has this degree of control over the temperature of high volume molten fly ash.
II. Description of the Prior Art
In the past, attempts have been made to utilize electronic furnaces to melt fly ash and produce mineral wool. For example, U.S. Pat. No. 2,817,695 issued to Hartwig discloses an electronic furnace and electrode structure designed for the melting of refractory materials such as mineral wool. Hartwig employs three main electrodes spaced 120 degrees from one another in a plane. A nozzle assembly is moveably positioned along a line perpendicular to the plane of the main electrodes at the center point of the three electrodes. The nozzle assembly is cooled below oxidation temperature by coolant flow in a nozzle support assembly.
Hartwig recognizes the need to provide accurate temperature control and attempts to accomplish this control by cooling the nozzle assembly and by supplying heat to the nozzle in accordance with temperature measurement of melted product passing through the nozzle assembly. Hartwig suggests that one way of achieving the requisite control is to apply an electrical potential between the nozzle and a selected one of the main electrodes to effect resistive heating of the melted product at the nozzle. However, except for stating that auxiliary power to the nozzle is turned on after the nozzle assembly has been properly positioned, Hartwig provides no teaching of how the suggested resistive heating of the melted product adjacent the nozzle is to be accomplished. Instead, Hartwig concentrates on the structure of coolant passages in the nozzle assembly.
U.S. Pat. No. 3,147,328 issued to Le Clerc deBussy discloses an electric glass making furnace which employs: three primary electrodes angularly spaced 120 degrees apart in a plane; a first conductive disc positioned along a line perpendicular to the plane of the main electrodes and which passes through the center of the three primary electrodes, and with the first disc having a passageway through which melted glass may pass out of the vessel; a plurality of auxiliary starting electrodes located above the plane of the three primary electrodes and moveably positioned adjacent the opening of the passageway in the first disc; and a second disc moveably positioned along the above-mentioned line of the first disc to form a slot between the first and second discs which slot is substantially on the same plane as the median plane of the primary electrodes.
In operation of the Le Clerc deBussy device, with the second disc in a separated position, the starting electrodes are moved together three centimeters from each other adjacent the opening of the passageway in the first disc, and are electrically energized to melt glass adjacent the first disc. The glass between the starting electrodes is also heated with a blow pipe. The starting electrodes are withdrawn as the glass begins to melt and the primary electrodes are energized. When the glass adjacent the first disc is in a liquid state, the second disc is brought into position above the first disc and is also supplied with electrical energy.
According to Le Clerc deBussy, in the course of normal operation, a major part of the current in the primary electrodes travels from a primary electrode through the glass, from the glass to the two discs, and then to the glass and finally to another primary electrode. The electrical circuit diagram supplied with Le Clerc deBussy shows the primary electrodes to be energized by a three-phased current source, and shows the first and second discs to be energized by single-phase current drawn from the main three-phase power supply.
Le Clerc deBussy recognizes that the hottest region in the molten glass is created between the two discs and the primary electrodes. However, the electrical and mechanical configuration of Le Clerc deBussy does not provide control of temperatures adjacent the passageway which would be sufficient to provide for high volume melting of fly ash is required in a high volume mineral wool manufacturing process. Instead, according to Le Clerc deBussy, only a small stream of glass is pulled through the slit between the two discs and sucked through the passageway of the first, lower, disc.
Other examples of electronic furnaces are provided by U.S. Pat. Nos. 3,876,817 and 3,659,029 also issued to Le Clerc deBussy and by U.S. Pat. No. 3,983,309 issued to Faulkner et al. However, none of these additional patents teaches a furnace arrangement or method of operation which provides for the required amount of temperature control to accomplish large scale melting of fly ash.
It is, therefore, an object of the present invention to provide a furnace and method of operation which can effectively convert large quantities of fly ash into mineral wool.
Another object of the present invention is to provide a furnace and method of operation which permits large scale conversion of fly ash into mineral wool through the use of multiphase electric current;
A further object of the present invention is to provide an electronic furnace and method which is capable of electronically generating a large amount of heat at a precisely controlled temperature over an exit orifice of a melting vessel in order to permit large amounts of fly ash immediately over that orifice to be raised to a precise temperature and to permit controlled flow of that fly ash through the orifice to produce large quantities of mineral wool.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.